There is growing interest in using biodegradable materials to replace permanent materials for many reconstruction applications. Degradable materials, however, are less stiff than permanent materials and suffer further stiffness reduction through time. Merely replacing the permanent material with a degradable material in the same design may lead to early device failure.
In light of the fact that many degradable materials lose material through bulk erosion without shape change, it is a principle of the present invention that through a topology optimization method accounting for base material degradation a degradable device may be created that retains sufficient stiffness through the degradation process. The optimization method of the present invention creates a density distribution map for selected time points during degradation. These different density distributions are then linearly superposed using both time and degraded base stiffness weighting factors.
According to the principles of the present invention, the present method is applied to design a degradable spinal fusion cage device from poly(propylene fumarate)/beta-tricalcium phosphate (PPF/β-TCP). However, the method is applicable for designing with any degradable material, such as but not limited to polylactic acid, polyglycolic acid, polycaprolactone, polyanhydride and tri-calcium phosphate.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.